Intrasexual Interactions Research Articles

How does former acquaintance affect aggressive behaviour in repeatedly mixed male and female pigs?

This study was undertaken to describe the effect of previous acquaintance on aggressive behaviour in repeatedly regrouped pigs and the nature of interaction between sexes. Four replicates of each 100 pigs (half entire males, half females) were weaned at 4 weeks and kept litterwise until 8 weeks, when they were randomly allocated to 10 pens of 10 pigs each. Random regrouping took place 4 times at 4 week intervals. In weeks 2–4 of each mix-period, aggressive behaviour was repeatedly recorded during feed competition. The dependent variables frequency and intensity of aggression were analysed (GLM-anova) in relation to class variables defined by combinations of acquaintanceship in litters and mix-periods. Additional class variables tested were intra and intersexual pairwise interactions (sex–classes). In mix-period 1 the frequency of aggression was significantly lower between littermates than between non-littermates (1.04±0.7 vs. 1.20±0.2, P=0.03), just as the intensity tended to be lower ( P=0.07). In mix-period 2 there was no longer any difference between littermates, nor any difference between pigs that had been together in the immediately preceding mix-period and those that had not. In mix-period 4 there was a tendency for pigs that had been together also in the preceding period to interact with higher intensity than those that had not been together. Intrasexual interactions between males and females did not differ, but the frequency of male-initiated intersexual interactions was significantly higher than female-initiated ones ( P=0.0001). No differences were found in intensity. The frequency of aggression declined over mix-periods ( P=0.005) which could be due to habituation or age, whereas the intensity increased ( P=0.0001), mainly due to female aggression towards males. The results of this study indicate that frequent regrouping seems to be a situation to which the social behaviour of the pig is not well adapted, and that the mechanisms whereby pigs recognise, assess and become familiar with strangers are disturbed. The found sex differences may, however, relate to the pigs' developmental stage.

Temperature modulates competitive behaviour: why sand goby males fight more in warmer water

An operational sex ratio is defined as the ratio of males to females ready to mate. Temperature has been shown to affect patterns of mating competition over the breeding season, as ambient water temperature differentially influences the potential reproductive rates of male and female sand gobies, Pomatoschistus minutus (Pallas), creating an unbiased operational sex ratio in colder water, and a male biased operational sex ratio in warmer water. Here, the direct effect of water temperature on frequencies of inter- and intrasexual interactions was studied in a short (24 hr) time perspective in aquaria with an unbiased adult sex ratio. Males were found to interact significantly more with other males, and also tended to interact more with females, in a warm (16 °C) water treatment, as compared with a cold (8 °C) treatment, even though there was no general increase in total number of interactions in the warm water treatment. Female-initiated interactions were not significantly affected by temperature. An altered operational sex ratio is unlikely to account for the observed difference in male-male interactions between treatments, for two reasons: (1) the operational sex ratio, which was estimated after the last behavioural recording in each replicate, was slightly, but equally, male biased in both treatments; (2) the operational sex ratio of each replicate was not correlated with the number of male-male interactions recorded from that replicate. Instead, these results suggest that temperature may influence the intensity of male mating competition directly, and I propose that individual fish use water temperature as a proximate cue for estimating and forecasting operational sex ratios.

TESTS FOR SEXUAL INCOMPATIBILITY BETWEEN TWO NEWT SPECIES, TRITURUS VULGARIS AND TRITURUS MONTANDONI: NO-CHOICE MATING DESIGN.

The evolutionary origin of reproductive isolation is still a source of considerable debate, although the consensus is that it develops by a gradual accumulation of genetic differences between populations, mostly in allopatry (Dobzhansky 1937; Muller 1942; Mayr 1963; Rice and Hostert 1993; Wu and Davies 1993; Templeton 1996). Quantitative studies of sexual isolation usually go no further than the calculation of the frequencies of homoand heterospecific matings; direct observations of courtship are rarely made (Spieth and Ringo 1983; Verrell and Arnold 1989). Consequently, relatively little is known about the role played by sexual behavior in maintaining reproductive barriers between species. Sexual isolation occurs when individuals tend to avoid mating with those of another strain, race, or species (Gilbert and Starmer 1985). Isolation estimates can be effected by mating propensity, or sexual vigor: the likelihood that a male or female will mate regardless of partner type. Moreover, mating propensity is likely to obscure estimates of asymmetry in sexual isolation unless controlled by experimental design or statistical analysis. Asymmetry is present when females from population A mate more frequently with males from population B than females from population B do with males from population A. Another source of error in both isolation and asymmetry estimates is the effect of social interactions. The most commonly used designs of mating experiments, in which individuals are given simultaneous choice of mates, do not control for intrasexual interactions and therefore can produce biased results (discussed in Arnold et al. 1996). We conducted a laboratory experiment with two species of European newts, the smooth newt, Triturus vulgaris, and Montandon's newt, T. montandoni, in which single males were paired with single females in a variety of crosses. This permitted a comparison of mating probabilities for four possible crosses. Our main goal was to determine the duration of courtships and identify the behavioral causes of sexual isolation. We also sought to demonstrate asymmetries at different stages of behavioral isolation between these two species. Although mating behavior of Triturus newts has been carefully described (Halliday 1977; Arntzen and Sparreboom 1989), surprisingly little information is available concerning the basis of sexual isolation between species. The genetic distance between T. vulgaris and T. montandoni is the lowest among species of the genus Triturus (DNei = 0.16; Rafin'ski and Arntzen 1987), and they readily hybridize in montane areas wherever they coexist (Hofmann 1908; Rafin'ski, unpubl. data). Old World newt species, including T. vulgaris and T. montandoni, possess elaborate and complex mating behavior that involves a prolonged male display followed by spermatophore transfer. Display consists of three distinct tail-movements produced by the male: whip, fan, and wiggle (detailed descriptions in Halliday 1974, 1975, 1976, 1977; Pecio and Rafin'ski 1985; Arntzen and Sparreboom 1989; Michalak 1996). Despite large differences in morphology of secondary sexual characters between the two species, there is only a slight difference in male courtship behavior, primarily in relative frequencies and duration of tail movements. In most cases the male initiates the courtship. The duration of display varies considerably and depends mainly on the reaction of the female. During spermatophore transfer, the female follows the male, walks over the spermatophore, and if her cloaca comes into contact with it, the spermatophore is then taken up into her cloaca. Cooperation on the female's part is an essential prerequisite both for spermatophore deposition and successful transfer. The onset of display, spermatophore deposition and transfer constitute distinctive events in the courtship of newts. Thus the composite courtship of newts provided us with an opportunity to analyze sexual isolation separately for the different mating phases.

Testosterone and mate choice in the dark-eyed junco

Investigations of the effects of testosterone on male mating effort have focused on behaviours associated with intra-sexual interactions. We tested whether testosterone may also affect male reproductive behaviour by mediating the intensity and frequency of male courtship. In two simultaneous choice experiments, we assessed the relative attractiveness of testosterone-implanted males, whose testosterone levels were manipulated to match naturally occurring spring peaks, and empty-implanted control males, whose testosterone levels were lower and resembled those of males caring for young. In both experiments, testosterone-males outperformed control-males, giving both more frequent and more exaggerated displays. Females showed a significant preference for the peak-testosterone males as measured by both female attendance and female courtship displays. We concluded that variation in testosterone can affect male attractiveness to females and thus male copulatory success. Thus, testosterone has the potential to mediate all aspects of male reproductive behaviour and may provide a mechanism through which males adjust their full range of breeding behaviours (i.e. inter-sexual as well as intra-sexual and parental behaviour) to fit their current status. In a second experiment, we tested the effect of oestradiol treatment on female mating preferences. No evidence was found that oestradiol changed the preferences of females.

Size‐dependent Mating Behaviours of Male Sand‐bubbler Crab, Scopimera globosa: Alternative Tactics in the Life History

AbstractFactors leading to the separation of mating behaviours were investigated in the sand‐bubbler crab, Scopimera globosa. The crabs mated on the surface (surface copulation, SC) and underground (UC). UC males were large (old) whilst SC males were small (young). Burrowless females bred in the UC males' burrows. These females accepted UC in exchange for access to a burrow. UC occurred much more frequently than SC in the burrow area in which females oviposited. Most SC occurred in the water‐saturated area affording a rich diet. SC was accepted by most large and small females in both areas and most UC by small females in the burrow area. SC was an alternative to UC for males in that there was a size dependence between types of copulation. These two mating behaviours involved different degrees of interaction with neighbouring males. Males attempting to carry a female to their burrows for UC were more often disturbed by other males than were males attempting SC. In the interaction for both UC and SC, larger males were likely to resist the disturbances. UC males needed their own burrows, but these burrows were not enlarged before mating. UC males have a higher paternity of eggs than SC males, because SC males' sperm is often displaced by other males. Thus, UC was a behaviour with relatively higher costs and benefits for male crabs than SC behaviour. Alternative mating behaviours in male S. globosa are conditional, and explained by intrasexual interactions and a male life history strategy with a trade‐off between growth and reproduction. It is not likely that the size dependence of male mating behaviour is caused by mate preference of females for UC males in the burrow area.

Why does dominance decline with age in wintering snow buntings?

The influence of sex and age on success in contests over access to food was studied in a wintering population of snow buntings,Plectrophenax nivalisin northeast Scotland over a 5-year period. Males won 87% of dyadic interactions with females, but, in contrast to many other studies, first-winter birds won a majority (60–70%) of intra-sexual interactions with same-sex adults. First-winter males continued to have greater success than adult males even after controlling for an individual's role within a contest, the degree to which the contest escalated, and the severity of the weather. Contests won by adult males were more likely to have escalated, perhaps indicating a greater cost, than those won by first-winter males. Dominance status dropped from an individual's first to its second winter of life, but not thereafter. It is argued that winning winter food fights is of more immediate benefit to first-winter birds, and that reversal of the usual age-related dominance pattern may be due to the species’ itinerant nature in winter combined with a lack of long-term pair-bonds or individual recognition. Assertion of dominance therefore carries only short-term benefits which may not override the costs of aggressive behaviour.

Acoustical Features of Song Categories of the Adelaide's Warbler (Dendroica adelaidae)

I identified acoustical features that distinguish the two song categories, A and B, of the Adelaide's Warbler (Dendroica adelaidae). Like many other wood-warbler species, male Adelaide's Warblers have functionally structured song repertoires such that A and B song categories are distinguished by common usage among males. The particular song types used in a given catego, however, vagreatly among individual males. Therefore, I focused my analysis on acoustical features other than song types. Song categories were distinguished by three major features: (1) the sound energy within a given B song was concentrated into a narrower frequency band, which was shifted about 600 Hz lower than for A songs; (2) the structure of B songs tended to be more complex, as they contained more note types and greater contrast between successive types than did A songs (discriminant function analysis using structural and frequency data correctly classified 85% of songs to catego); and (3) the singing behavior associated with B-song sequences was more complex, due to inclusion of a larger number of song types, more frequent switching or alternating between them, and a more rapid rate of song deliver. Overall, the B categoappears to represent a more complex and lower frequency signal than the A catego. Differences between the two song categories, which parallel data available for other paruline species, should reduce signal ambiguity and are consistent with several nonmutually exclusive functional interpretations: The B-song catego, used in intrasexual interactions, might represent a more aggressive signal or might be specialized for caring motivational information. Females might find the higher-fre- quency A-song categomore appeasing or stimulating. Song categories A and B also might be specialized for traveling different distances, at different times of day, or through different microhabitats. Received 5 December 1994, accepted 16 February 1995.

Subadult Plumage in the House Finch and Tests of Models for the Evolution of Delayed Plumage Maturation

-In many passerine species males do not attain definitive breeding plumage until after their first potential breeding season. Such delayed plumage maturation has been the subject of numerous studies, most of which have focused on the adaptive value of femalelike plumage for young males in single populations. Thus, although studies of delayed plumage maturation have been presented as tests of evolutionary hypotheses, most have lacked an appropriate comparative perspective. Moreover, most studies of subadult plumage in passerines have been conducted without information on the general function of ornamental plumage in the species being studied. A study of delayed plumage maturation in the House Finch (Carpodacus mexicanus) provided an opportunity to overcome these problems. The function and proximate control of ornamental plumage coloration in House Finches have been studied extensively. In addition, House Finches occupy a wide range across North America with approximately 15 subspecies recognized, and populations vary in expression of delayed plumage maturation. In most populations, including the most familiar subspecies, C. m. frontalis, males acquire definitive basic plumage in their first prebasic molt. In at least three populations, C. m. griscomi of southern Mexico, C. m. amplus of Guadalupe Island, and Great Basin populations of C. m. frontalis, however, males do not acquire definitive plumage until the completion of their second prebasic molt, spending their first potential breeding season in a female-like plumage. Using a composite phylogeny and parsimony analysis, I show that delayed plumage maturation likely was lost in the ancestral House Finch population and was regained independently by the three taxa in which it is now observed. Thus, delayed plumage maturation in the House Finch is a derived trait. In addition, I show that the acquisition of delayed plumage maturation is associated with a reduction in the extent of ornamental plumage (i.e. a reduction in patch size). These observations support the idea that delayed plumage maturation in the House Finch is an adaptation to increased production costs of red ornamental display plumage in some populations. Received 28 November 1995, accepted 25 April 1996. DELAYED PLUMAGE MATURATION describes a developmental pattern generally limited to males, whereby individuals do not acquire definitive breeding plumage until after their first potential breeding season (Rohwer et al. 1980, Rohwer and Butcher 1988). Studies of delayed plumage maturation most frequently concern Temperate Zone passerines that spend only one potential breeding season in a subadult plumage (Rohwer and Butcher 1988, Butcher and Rohwer 1989, Zack and Stutchbury 1992). Despite a substantial literature on delayed plumage maturation (see Zack and Stutchbury 1992), our understanding has advanced relatively little since interest in the topic was first ignited by Rohwer et al. (1980). I believe that the ma1 E-mail: geoffrey.hill@ag.auburn.edu jority of research on delayed plumage maturation in passerines suffers from two fundamental problems: (1) lack of a general understanding of the function of ornamental plumage coloration, and (2) lack of an appropriate comparative approach to testing hypotheses for the evolution of delayed plumage maturation. The first of these problems clearly is a case of putting the cart before the horse. Ornamental plumage coloration, either bright structural coloration, bright carotenoid-based coloration, or highly contrasting melanin-based coloration, is universally assumed to function as a signal in avian communication (Butcher and Rohwer 1989). Signaling generally is believed to occur in the context of either intersexual or intrasexual interactions (Butcher and Rohwer 1989), but predator-prey interactions also have been considered (Gotmark 1992, 1993). An assump-

Size assessment via a visual signal in snapping shrimp

Snapping shrimp are highly aggressive decapod crustaceans, with large, asymmetric chelae. Body size determines the outcome of both inter- and intrasexual interactions. Both the body and chela sizes of mated pairs are correlated, but the body size correlation is significantly stronger. In competitive interactions between individuals of the same sex, larger individuals usually win. Because the size of the major chela is a function of body size in both males and females, chela size could be used to assess body size early in interactions, before engaging in more high risk behaviors. To determine whether the major chela is used in size assessment, I presented shrimp with isolated chelae. Male snapping shrimp responded aggressively to isolated chelae when they were fixed open in a display posture, and the degree of aggressive response depended on the relative size of the chela. These data provide direct experimental evidence for the use of a visual signal in size assessment. Females, in contrast, responded aggressively to both the open and closed chela, and their responses did not depend on relative size. This sex difference in response may be due to differences in the value of certain resources, such as shelters, to males and females: females may be more willing to respond aggressively regardless of the apparent size of their opponent, in order to acquire more reliable information regarding size, motivation or fighting ability.

Chest plumage, dominance and fluctuating asymmetry in female starlings

It has been proposed that levels of fluctuating asymmetry (FA) may be used in establishing and maintaining dominance hierarchies, as asymmetry reflects aspects of individual quality. However, previous manipulations of FA have failed to reveal that the level or outcome of agonistic intra-sexual interactions are affected by levels of FA. In female European starlings (Sturnus vulgaris), correlational data suggest that FA of the speckled chest plumage may be related to dominance status. These data are confounded, however, by total number of spots on the chest and the proportion of the chest that is white, both of which positively covary with chest asymmetry. Thus, we deconfounded the effects of these plumage traits on dominance by experimentally manipulating the number of spots and spot number asymmetry in a factorial design. The results indicated that dominance is influenced by the number of spots on the chest, but not by spot asymmetry. Birds with spottier chests were dominant over birds with experimentally decreased spot number. We suggest that female starlings' chests are exposed to extensive abrasion throughout the breeding season and so are susceptible to damage asymmetries that may mask the `true' fluctuating asymmetry of the trait. This may devalue the use of chest asymmetry as a quality indicator. Spottier chests may be costly to maintain, in part because of increased susceptibility to abrasion, and so may be a better indicator of quality than asymmetry.

Sexual competition and courtship disruptions: why do male bowerbirds destroy each other's bowers?

Abstract. In the species of bowerbirds that build bowers, males frequently attempt to maraud and destroy each other's bowers and steal decorations. A series of game-theory models was developed to examine disruptive behaviour in bowerbirds under different mechanisms of male choice. By measuring the costs and benefits of alternative behaviour patterns in terms of access to females, the models demonstrate that, under most circumstances, strategies of marauding bowers and/or stealing decorations are stable against a strategy of guarding bowers and not disrupting. The range of conditions in which guarding was stable increased if intruders had to travel long distances between bowers or if residents were able to quickly repair damaged bowers. Male bowerbirds, however, may be in a prisoner's dilemma with respect to disruptive behaviour patterns. That is, marauding and/or stealing are always the best individual strategies, but neighbouring males that guard their bowers and do not disrupt each other always do better than neighbouring males that disrupt each other. Under these circumstances, conditional strategies may evolve and one such tactic that bowerbirds may employ is discussed. It is suggested that the nature of bower-building and the importance of bowers in inter- and intra-sexual interactions dramatically affect each species' behavioural and activity patterns, spatial dispersion, and social organization.

Sex recognition and the role of urinary cues in the lobster,Homarus americanus

Components of sex recognition by American lobsters, Homarus americanus, have been characterized by detailed study of videotaped recordings of both intra‐ and intersexual interactions in temporarily blinded lobsters. These analyses have permitted us to describe behaviors typically displayed by lobsters in agonistic intrasexual interactions in the absence of visual cues. The results suggest that sex recognition occurring over short distances may not rely on visual information. A method of antennal gland cannulation was developed that allowed for continuous collection of voided urine from individual lobsters in paired interactions away from contact with the seawater. Normal behavior patterns were observed in all intra‐and intersexual pairings of lobsters. Courtship and mating also occurred when either or both intermolt male and postmolt female were cannulated indicating that urine is not a source of factors required for lobster sex recognition.

Context and consequences of comb displays by male rock ptarmigan

Abstract. Male rock ptarmigan, Lagopus mutus, display their supraorbital combs for about 50% of the time during both inter- and intra-sexual interactions in the breeding season, but rarely when they are alone. During three seasons in the Canadian high arctic, mating success of male rock ptarmigan was positively correlated with both comb condition and previous breeding experience. There was no general relationship between a male's comb size and his mating success, contrary to results obtained in both a previous study in this same population and experimental studies on other species with combs. There was, however, a correlation between comb size and mating success among inexperienced males that may explain the results from other studies. Model presentation experiments also revealed significant relationships between comb condition, comb size and aggressiveness, such that males with smaller combs or combs in poor condition were less likely to attack male models with artificial combs. The size of model combs, however, had no influence on male aggressiveness. Because combs are frequently attacked during male × male interactions, the condition of these ornaments may honestly advertise male fighting ability and as a result may be an important criterion for female choice.

Correlates of Agonistic Display By Great Tits Parus Major

This study examined physical and social correlates of agonistic display performance by wild great tits Parus major competing over food and territorial space. All behavioural data were collected at winter feeding stations from individually colour-ringed birds for which data on physical characteristics, current social status and individual history were available. At feeders, competitive interactions between males were more frequent than those involving females, and birds not present in previous winters (mostly first-winter birds) interacted more frequently than prior residents (locally territorial adults). Interactions away from food sources usually involved at least one male, increased in frequency over the course of the winter, and often involved chasing of one bird by another. These interactions are thought to reflect competition for territorial space. Males were almost always dominant over females in competitive interactions. Simple supplants were most frequent in intersexual interactions, with display being more often seen in interactions between birds of the same sex. In intrasexual interactions, there were no consistent differences between the sexes in frequency of use of displays, but there was a general trend for postural display elements to be performed more often by eventual dominants than by eventual subordinates. Displays based on 'head-up' tended to be performed by prior resident, locally dominant, territorial males. Their incidence increased over the course of the winter, and they were especially associated with non-feeder interactions. Displays based on 'wings-out' and 'tail-fanning' were associated with non-territorial, first-year birds that were less frequently occurring at the study site, and tended to occur in cases where the opponents had little prior experience of each other. Displays based on head up were performed almost exclusively in intraspecific interactions, whereas those based on wings out and tail fanning were also common in contests over food with blue P. caeruleus and coal tits P. ater, in which the great tit was usually dominant.

Courtship and agonistic behavior in mouflon sheep

Although native to Corsica and Sardinia, mouflon sheep ( Ovis orientalis musimon) have been widely introduced to other areas, including the United States. This study examines the courtship and agonistic behavior of 2 captive mixed-sex herds in west-central Texas, U.S.A. These herds were observed in large enclosures on game ranches during the autumn of 1980. Inter- or intra-sexual interactions consisted of one or more repeated behavioral postures (i.e. low stretch, twist, foreleg kick, sniff rear, urination, flehmen, mount, horn threat, chest push, neck fighting, head butt, clash, horn rubbing, chase). Ninety-five male-male, 63 female-female and 155 male-female interactions were observed. Low intensity agonistic displays (with total number of occurrences in the interactions given in paren-theses) such as foreleg kicks (154) and twists (141) were most frequently seen in male-male interactions. Although head butting (96) was commonly observed in male-male encounters, clashes (52) were also prominent. In female-female agonistic interactions, an unexpectedly high frequency of head butts (99) were regularly exhibited. Agonistic and courtship behavior patterns such as twist (131) and flehmen (106) were prominent in the behavior of males toward females. Although males would occasionally head butt a female (22), they seemed to inhibit clashing in their interactions with the hornless females. In most cases, female-female interactions were initiated by head butts (46) and male-male encounters began with either a head butt (23) or twist (18). Male-female interactions showed more variation in the behaviors which initiated the encounter, but usually began with a twist (39), flehmen (29) or low stretch (20) by the male. The observations of mouflon in this study conformed well with previous reports of sheep behavior.

The complex communicatory behaviour ofMarpissa marina, a New Zealand jumping spider (Araneae: Salticidae)

Abstract This is the first study of the complex display repertoire of Marpissa marina, a New Zealand jumping spider. The adaptive significance of this species’ complex repertoire is discussed. Males are shown to employ two types of courtship and three mating tactics, depending on the location and maturity of the females they encounter. They court adult females outside nests with visual displays (type 1 courtship) and mate in the open (tactic No. 1). They court females inside nests with vibratory displays (type 2 courtship) and mate with adult females in their nests immediately after courtship (tactic No. 2); but build a second chamber on subadult females’ nests in which to cohabit, then mate with these females after they mature (tactic No. 3). Rotary waving of the abdomen, a display that is apparently unique to this species, is described. Only males perform this behaviour, and they do so only when touching a female in a nest. Displays during intrasexual interactions are distinct from courtship displays. M. marina’s most elaborate display is quadrapedal posturing, which is performed only during male-male interactions. New Zealand has a depauperate salticid fauna and no other salticid species were found sharing M. marina’s microhabitat, lending no support to the prevalent hypothesis that display complexity in spiders is related to species identification. We propose, instead, that sexual selection has been the major factor responsible for M. marina’s display complexity.

Testosterone and survival: A cost of aggressiveness?

Free-living male brown-headed cowbirds were captured during the breeding season, implanted with testosterone-filled Silastic tubing, and released. Radioimmunoassay verified that the implants maintained circulating plasma testosterone values at maximal breeding season levels well beyond the normal time of decline. Survival to the following year of these implanted males was compared with survival of unimplanted birds captured in other years, and also with survival of males given empty implants. Androgen-implanted male cowbirds exhibited significantly reduced survival to the following year compared with either of the control groups, and also exhibited severe injuries not seen in other years. It is suggested that the increased risks associated with prolonged high testosterone levels act as a selective force to maintain reduced androgen levels except during the period of aggressive intrasexual interactions that characterizes the reproductive season. Further, it is proposed that the nature and importance of the different risks vary with a species' mating system.

Responses of a Population of California Voles, Microtus californicus, to Odor-Baited Traps

Individuals in a wild population of California voles ( Microtus californicus ) were presented with a choice between clean and odor-baited traps to determine patterns of investigation or avoidance of conspecific odors by various sex and age groups in the field in both breeding and non-breeding seasons. Adult California voles captured during the breeding season showed strong patterns of attraction to live-traps containing conspecific odors. Voles captured during the non-breeding season and juveniles captured during the breeding season did not show a preference for odor-baited traps. During the breeding season, large males and all adult females were attracted to both male and female odors. Smaller males were attracted to female odors only. These results indicate that intrasexual interactions may be stronger among male than among female M. californicus . However, territorial behavior among females is probably more well-developed than previously suggested for this species. Results of the present study and other studies utilizing odor-baited traps indicate that using soiled traps may violate the assumption of equal trappability of all individuals that is inherent in most density estimation techniques. While a greater number of animals might be attracted to soiled traps, a more accurate demographic cross section might be obtained if all traps were kept clean.

Inter- and intra-sexual interactions in a New Guinea skink, Emoia physicae

Three experiments were conducted in outdoor arenas with a small, New Guinea skink, Emoia physicae, to examine inter- and intra-sexual interactions. There were statistically significant differences in behaviour between adult males and adult females and in interactions within the sexes. Within sexes, larger lizards dominated smaller ones. Females dominated males, even though females are smaller. Intrasexual encounters were more likely to be agonistic than were intersexual encounters. Intrasexual encounters were more likely to be overtly agonistic among males than among females, but females often avoided one another. Both sexes of E. physicae exhibit behaviors that could function in a territorial context.

Sexual Monomorphism in Spotted Hyenas, Crocuta crocuta

AbstractIntersexual and intrasexual interactions by female spotted hyenas, (Crocuta crocuta), are correlated with the ability of the heavier and more aggressive females to dominate males at large carcasses, the principal food of spotted hyenas.Female spotted hyenas have a modified clitoris closely resembling a penis. A slightly bilobed scrotum containing fat and connective tissue contributes to the male‐like appearance of the female sexual facies. Penile and pseudopenis erection by spotted hyenas occurs primarily during social encounters at carcasses and elsewhere.Analyses here, based on interspecies comparisons of spotted hyena, brown hyena (Hyaena brunnea) and striped hyena (H. hyaena) morphology, behavior and ecology and interpopulation comparisons of spotted hyenas suggest possible gradualistic evolutionary interpretations of the pseudopenis.